Grinding of materials with hard abrasives



F 1966 c. W. HlGHBERG 3,233,369

GRINDING OF MATERIALS WITH HARD ABRASIVES Filed May 11, 1962 4Sheets-Sheet 1 GRINDING HARD BRASIVE SEGMENTS GRIT 72 SEGMENT HOLDERSINVENTOR. CARLE W- HIGHBERG TORNEY Feb. 8, 1966 C. W. HIGHBERG GRINDINGOF MATERIALS WITH HARD ABRASIVES Filed May 11, 1962 FIG.6 V

4 Sheets-Sheet 2 SPINDLE DIAMOND FIG.7

GRINDING WHEEL 5| 4 OF COOLANT FLOW COOLANT SUPPLY/ TANK 23 PUMP ORIFICEFOR COOLAN'II5O 48 ORIFICE FOR COO LAN T a ,a

DIAMOND GRINDING SEGMENT 52 GRINDING MATRIX DIRECTION OF COOLANT FLOW II III 52 CARLE w. HI

Feb. 8, 1966 c. w. HIGHBERG 3,233,369

GRINDING OF MATERIALS WITH HARD ABRASIVES Filed May 11, 1962 4SheetsSheet 3 MELTING FURNACEI I ANNEALING CHAMBERJ INITIAL DIAMONDGRINDING STATIONS LOW CONCENTRATIONS OF DIAMONDS DIAMOND ADDITIONALSUCCESSIVE DIAMOND GRIND- GRlNDING- ING STATIONS-HIGHER CONCENTRATIONSOF 'gk g ggig STATIONS DIAMONDS THAN IN INITIAL STATIONS LATE DIAMONDGRINDING STATIONS LOW CONCENTRATIONS OF DIAMONDS MATERIALLY LOWER THANIN THE ADDITIONAL SUCCESSIVE STAGES IRON OXIDE POLISHING i J TRANSFERAND REVERSAL T INITIAL DIAMOND GRINDING STATIONS LOW CONCENTRATIONS OFDIAMONDS DIAMOND ADDITIONAL SUCCESSIVE DIAMOND GRIND- GRINDING INGSTATIONS-HIGHER CONCENTRATIONS OF g E k STATIONS DIAMONDS THAN ININITIAL STATIONS LATE DIAMOND GRINDING STATIONS LOW CONCENTRATIONS OFDIAMONDS MATERIALLY LOWER THAN IN THE ADDITIONAL SUCCESSIVE STAGES [TRONOXIDE POLISHING INVENTOR. CARLE W. HIGHBERG TTORNEY Feb. 8, 1966 c, w.HBER 3,233,369

GRINDING OF MATERIALS WITH HARD ABRASIVES Filed May 11, 1962 4Sheets-Sheet 4 F|G.9 M T R SPINDLE T 1 HOUSING GLASS I l DRIVING 22SHEET ROLLERS GRINDNG L WHEEL 21 GLASS 2 COOLANT SHEET l5 TANK 28 FIG.ll

INVENTOR. CARLE W. HIGHBERG ATTORNEY United States Patent 3,233,369GRINDING OF MATERIALS WITH HARD ABRASTVES Carle W. Highberg, MurrayHill, N.J., assignor to Engelhard Hanovia, Inc., Newark, N.J., acorporation of New Jersey Filed May 11, 1962, Ser. No. 193,925 Claims.(Cl. 51-110) This is a continuation-in-part of my copending applica-.tion Serial No. 119,444, filed June 26, 1961, now Patents No.3,177,628.

This invention relates in general to the grinding of materials with hardabrasives, and more particularly, to a new and improved method andapparatus for grinding and/or honing of surfaces or edges of materialssuch as, for instance, glass, stone, ceramics, cemented carbides andferrous metals.

As is developed hereinafter, the studies which led to the broad conceptsof the present invention have been generally carried out on the specialapplication of grinding glass with diamond grinding wheels. However, itis to be understood that the principles of this invention are notrestricted to only diamond grinding of glass but are equally applicableto the grinding of various other materials, for instance stone, e.g.,marble, granite, etc., ceramics, e.g., silicon carbide (Carborundum),aluminum oxide, etc., cemented carbides, e.g., tungsten carbide, andferrous metals, e.g., hard steels containing V, W, Cr, Co, orcombination of these alloying metals, employing hard abrasives otherthan diamonds, for instance cubic boron nitride.

In the prior art manufacture of plate glass, the plate is continuouslyextruded from the melting furnace, followed by passage through anannealing chamber. From the annealing chamber, the plate glass issubjected to grinding and polishing, typically involving passage firstthrough twenty eight successive beach sand grinding stations. Thegrinding operation is carried out at each of these stations by largegrinding heads having vertically mounted spindles, which have horizontalgrinding surface extending across the width of the plate glass. Afterthe grinding at such beach sand stations, additional polishing isrequired, typically at forty two additional stations, wherein thepolishing heads also have vertical spindles, and iron oxide or rouge isemployed as abrasive. This prior art process for grinding plate glass isdisadvantageous for the reasons that a large amount of expensivemachinery and floor space is required, and the facilities and manpowerrequired for handling the bulky abrasive are very costly.

In my co-pending application Serial No. 50,352, filed August 18, 1960,now abandoned, a considerable improvement in the grinding and polishingof glass is provided by the replacement of the first two-thirds or moreof such seventy stations of grinding and polishing with a lesser number,such as or less stations of diamond grinding. This large reduction inthe number of grinding stations required was achieved by the use ofdiamond grits or particles in the surface portion of the grinding headsinstead of the beach sand. This method is a considerable improvement forthe reasons that the amount of floor space, machinery and manpowerrequired in the processing of the plate glass is considerably reduced,with resulting reduced cost of the entire operation. In this improve-Patented Feb. 8, 1966 ment method, the diamond concentration in terms ofcarats per cubic inch of grinding wheel matrix is relatively low in theinitial stations of rough grinding and is increased in the additionalsuccessive grinding stages and later stages with a correspondingreduction in diamond particle size, the diamond concentrations being thelargest or highest in the late stages.

A further improvement in the grinding of glass over that of applicationSerial No. 50,352 is disclosed and claimed in my copending applicationSerial No. 119,444, filed June 26, 1961. In the method of applicationSerial No. 119,444, diamond grinding of the glass is carried out ininitial stations with wheels having a low concentration of diamonds ofpredetermined grit size, followed by diamond grinding the glass inadditional successive stations with wheels having higher concentrationsof smaller grit size diamonds than in the initial stations, and diamondgrinding the glass in late stations with wheels having low diamondconcentrations materially lower than those of the wheels of theadditional successive stations and which can also be materially lowerthan the diamond concentrations of the wheels of the initial stations,the diamond grits of the wheels of the late stations being of stillsmaller grit size. The grinding wheels employed in all stations have apredetermined concentration of diamond grits bonded in the leading andtrailing edges of the Wheel, and these predetermined grit concentrationsat the wheel leading and trailing edges should be controlled withinclose limits to obtain optimum results. It was also found that thepresence of a predetermined concentration of diamond grits bonded in thewheel intermediate cutting surface, i.e., the cutting surface or facebetween the leading and trailing edges of the wheel, was of importancefor obtaining good results. The method and apparatus of this applicationachieve a striking economy in the quantity of diamonds required and aconsiderable reduction inoverall costs as Well as a considerableprolonging of the life of the grinding wheel, reduction in breakage anddamage to the glass, and obtainment of grinding results that arepredictable and can be duplicated. In a preferred embodiment ofapplication Serial No. 119,444, the grinding wheels are segmented withthe grinding segments being arranged on the wheel support in a generallycircular arrangement preferably adjacent the peripheral edge portion ofthe support. The grinding segments each comprise a matrix having diamondgrits bonded therein. More preferably the grinding segments are arrangedon the wheel support in a continuous narrow arrangement with minimumspacing between neighboring segment edge portions. By reason of thiscircular arrangement of the segments on the wheel support, aconsiderably prolonged life of the wheel is achieved.

In accordance with the present invention, it has been found that thecombination of (1) grooved grinding wheels, preferably radially groovedwheels with a metal matrix bonding the grits, (2) hard abrasive grits onthese grooved wheels of preferably a grit size of 200230 grit size orfiner, more preferably within the range of 500 2500 grit size, and (3)liquid coolant supplied to the wheels during the surfacing resulted in asignificant improvement in the surfacing of the plate glass at latestations of the grinding method of application Serial No. 119,444.Narrow grooves are generally used as will be u? specifically discussedhereinafter, relatively wide grooves having little or no advantage.Further, unnecessary width of grooves cuts down on the availablegrinding surface. This combination of the three features mentioned aboveof this invention significantly improved the plate glass surfacing at avariety of grit sizes within these ranges.

In the grit size range of 5002500 grit size, grit sizes of the abrasivewithin the range of 1050-1500 grit size are especially preferred.

The grinding apparatus of this invention comprises a rotatable spindle,a grinding wheel mounted on the spindle, means for rotating the spindleand hence the grinding wheel, and means for feeding plate glass throughthe apparatus for surfacing by the wheel. The grinding wheel comprises asupport member, a matrix preferably of metal on the support memberproviding a grinding surface, and means for securing the matrix to thesupport. A plurality of spaced grooves are provided in the grindingsurface, diamond grits or grits of other hard abrasive materialshereinafter disclosed and of the grit size previously disclosed arebonded in the metal matrix, and means are provided for supplying aliquid coolant to the wheel, preferably to its inner grinding edge.

The grooves employed are preferably radial; i.e., extending outwardly inradial fashion with the center of the wheel their origin if they wereextended inwardly this extent. However, in addition to the radialgrooves, concentric grooves can be utilized, i.e., grooves arrangedconcentrically with respect to the center of the wheel and one anotherin the grin-ding surface. Concentric grooves may be desirableparticularly where the grinding surface radial dimension is large andsuch concentric grooves would suitably intersect the radial grooves. Thegrooves are equally or substantially equally spaced in the wheelgrinding surface and preferably extend from the inner to the outer edgesof the cutting surfaces.

Width of the grooves is related to size of the abrasive grits used. Ingeneral, the use of coarser abrasive grits requires greater widthgrooves and smaller size grits narrower width grooves. For instance, for12 foot diameter wheels, grooves having width of preferably from about.005"-.023 are employed when grits of particle size of about 8-25microns 1050 grit size) are used, and grooves of width of preferablyfrom about .010".045" are employed when larger size grits of particlesize of about 30-50 microns (500 grit size) are used.

The grooves can be provided in the wheel grinding surface after thewheel has been made by cutting by means of any suitable cutting toolwell known to those skilled in the art, or by spacing the abrasivesegments, usually pres ent in wheels over 18 inch outer diameter, asufficient distance when mounting same on the wheel holder to providethe grooves. Thus the term groove or grooves is used in a broad senseherein to include not only grooves provided in the grinding surface bycutting, gouging, etc., but also provided by spacing apart the abrasivesegments the desired distance, or by the combination of cutting,gouging, etc., and the spacing apart of the abrasive segments.

The shape of the grooves is an important consideration. V-shaped groovesas will be shown in the embodiment of this invention of FIG. 4 may beused, but it is preferred to work with flat-bottomed grooves of uniformor substantially uniform width since in such case the groove width doesnot change as the grinding surface wears away.

While it is not definitely known why or how these grooves exert theirbeneficial effect, one plausible explanation is that the grooves serveto aid in the removal of the abrasive debris from the wheel cuttingsurface. The :presence of this abrasion debris has resulted inunsatisfactory results heretofore when wheels with 1050 grit sizeabrasives and a diamond concentration of 0.25 carats/cu. in. were used.In fact, such wheels could not be operated even at nominal downfeedswithout excessive burnishing of the glass. The cause of this difficultyhas been attributed to the lodging of abrasion or grinding debris on orcontiguous to the cutting surface of the wheel. Further, when 2500 gritsize diamond wheels were used, the metal bond or matrix utilizedactually became embedded in the glass at nominal glass removals and nogrinding could be accomplished. However, the presence of the groovesspaced preferably radially at equal or substantially equal intervals onthe grinding heel having the fine abrasive particles or grits inaccordance with this invention results in superior grinding wheel life,and in superior surface finish of the material being ground andpolished. It also enables satisfactory and economical use of wheels withparticle size abrasives of 1050 grit size (825 micron size), whereasformerly such wheels could not be operated satisfactorily. It also makespossible the use of wheels with finer size abrasives than 1050 gritsize. Specifically, in accordance with this invention, it has been foundthat wheel life of 3,000 cubic inches of glass/ carat or greater can beplanned on and attained for plate glass surfacing with diamond gritsizes of this invention including 1050 grit size, at the usual downfeedsor glass removal rates employed with such grit size wheels.

The width of the grooves, in addition to being a function of the size ofthe abrasive grits used, is also a function of wheel size with widergrooves utilized with smaller size wheels and narrower grooves employedwith larger size wheels. The grooves must be of sufficient size to clearaway abrasion or grinding debris. However, the groove width should notbe so large that the diminution of the concentration of the particles atthe leading and trailing edge of the wheel is such that it lowers thegrinding life of the wheel. In typical runs, grooves A th inch in widthwere found advantageous in wheels with 200-230, 500 and 1050 grit sizediamonds in wheels of 3 inch O.D. (i.e., outer diameter) and 30 inchO.D. However, in larger size wheels such as for instance a 12 foot O.D.wheel with 1500 grit size diamonds, grooves smaller than th inch andtypically 0.009 inch in width are preferred.

The frequency of grooves required for optimum performance is also afunction of the grit or particle size and the Wheel size. For a givengrit size, the number of grooves required increases with the size of thewheel. For example, with diamond wheels operated at about 2850 surfacefeet per minute, favorable grinding with 500 grit size diamonds wasobserved with 3 inch O.D. cup wheels containing four grooves each of thinch width and with 30 inch O.D. segmented wheels contain-f ing 96grooves each of th inch width. The optimum frequency of the grooves fora particular wheel size increases with the decrease in particle or gritsize. For instance, it has been found that with three inch O.D. cupwheels with th inch width radial grooves, the optimum number of grooveswas as follows:

Grit size: Optimum number of grooves 500 4 1050 8 1500 16 There is adisadvantage in increasing the number of grooves over certain values forgiven wheels. Once the grooves are present in such quantity as to permitsuflicient coolant to contact the cutting surface of the wheel,additional grooves may materially sacrifice the concentration of diamondgrit in the leading and trailing edges of the wheel with resultant lossof diamond life of the wheel.

Coolant is employed for absorbing heat from the grinding surface, whichimproves the life of the grinding wheel, and this coolant is preferablydelivered or supplied to the inner cutting edge of the wheel, suchdelivery of the coolant being of considerable importance to theperformance of the diamond wheels. It was found that by reason ofsupplying the coolant to the inner cutting edge of the wheel, thecoolant is most efficiently utilized in contrast to delivery of thecoolant to the outer cutting edge of the wheel which gives lessefficient use of the coolant. By the interior delivery of the coolant,centrifugal force causes it to contact all the exposed diamond gritsurface, provided the segments are placed with minimum spaces betweenthem. However, panticularly with large grinding wheels, it may be usefulalso to apply coolant to the outer cutting edges. The coolant can besupplied to the inner cutting edge of the wheel by means of a hollowshaft spindle, or with larger wheels preferably by flowing down theinner edges of the grinding segments through suitably disposed orificesor holes in the diamond Wheel. The coolant is an oil in water emulsiontype and preferably comprises, by volume, from about 20 100 parts ofWater per each one part of coolant concentrate (oil and emulsifier).

For use with the coolant and grooves, wheels having the diamond gritsbonded thereto with metal are preferred. Among these metal bondedWheels, a copper-based alloy, i.e., an alloy containing a majorproportion of copper is the preferred bonding material or matrix. Inaddition to the copper, other metals advantageously present in the alloyof the bonding material or matrix include one or more of zinc, tin,silver, aluminum, beryllium, manganese and iron. Brasses and bronzes areparticularly suitable. A typical analysis of one brass matrix Wellsuited for use in the grinding wheels of this invention for bonding thediamond grits is the following:

Element: By weight Copper, 70 Zinc, 30

A typical analysis of one bronze matrix well suited for use in bondingthe diamond grits in the wheels is the following:

Element: By Weigh Copper, 80 Tin, 20

Extension of Mohs Scale Metal Equivalent Mohs Scale Orthoclase orpericlase Vitreous pm'e silica (7) Quartz. (8) Topaz.

(l1) Tantalum carbide (12) Tungsten carbide (9) Sapphire.

(6) Orthoclase.

(10) Diamond.

This tabulation is adapted from Ridgeway et al., Trans. Electrochem.Soc. 63, 369 (1933). by addition of cubic boron nitride at a numberhardness as equivalent to diamond.

As set forth in the foregoing tabulation, materials having a hardnessnumber of 8 and higher on the Extension of Mohs Scale include quartz,topaz, garnet, fused zirconia, fused alumina, silicon carbide, boroncarbide, diamond and cubic boron nitride. In the Metal Equivalentcolumn, stellite has a hardness number of 8 which is equivalent to thatof quartz, tantalum carbide has a hardness of 11 which is equivalent tothat of fused zirconia, and tungsten carbide has a hardness of 12 whichis equivalent to that of fused alumina or sapphire. It is known thatcubic boron nitride will scnatch diamond and that diamond will scratchcubic boron nitride, so that they are properly considered as equivalentin hardness.

The disclosures herein of preferred diamond concentrations for thegrinding, and in particular surprisingly low diamond concentrations inlate stages of grinding glass are not restricted to diamond grinding ofglass. These surprising results are obtained also in the grinding ofvarious other materials, for instance stone and ceramics, with otherhard abrasives such as those enumerated above having a hardness of 8 orhigher, preferably 12 or higher on the Extension of Mohs Scale,preferably when the abrasive is used in a grinding wheel and a coolantis employed. A particularly effective hard abrasive other than diamondis cubic boron nitride. Stone which can be ground in accordance with thepresent invention includes marble, granite, etc. and ceramics which canbe ground include silicon carbide (Carborundum), aluminum oxide, etc.

Diamonds are now available from both natural and synthetic sources, butcubic boron nitride is solely a synthetic product. Synthetic diamondsand synthetic cubic boron nitride are known to be produced by use ofhigh pressure, greater than 30,000 atmospheres, with catalyticpromotion. successful chemical production of synthetic cubic boronnitride without use of high pressure. It is reasonably possible that inthe near future cubic boron nitride may e available at a lower pricethan diamonds. Cubic boron nitride is described by R. H. Wentorf, Jr.,in J. Chem. Phys. 26, 956 (1957).

In the drawings:

FIGURE 1 is a plan view of a grooved, segmented grinding or surfacingwheel of this invention;

FIGURE 2 is a section taken on line 22 of FIG URE 1;

FIGURE 3 represents an enlargement of a portion of the wheel of FIGURE1;

FIGURE 4 is a section taken on line 4-4 of FIG- URE 3;

FIGURE 5 is a plan view of a grooved cup wheel of this invention, whichcup wheel is a smaller wheel than the segmented wheel of FIGURE 1;

FIGURE 6 is an elevational section through the hollow shaft spindle of agrinding wheel of the present invention, the coolant being supplied tothe inner cutting edge of the wheel through the enclosed centralpassageway of the hollow spindle, this figure also showing the pump andconduit for supplying the coolant from the coolant supply tank to thehollow shaft spindle;

FIGURE 7 is an elevational section through the spindle and grindingwheel of a larger grinding wheel of the invention and showingcoolant-supply orifices or holes in the wheel support, these orificescommunicating with a coolant-supply conduit leading from acoolant-supply tank, this figure also showing the coolant-supply tankand pump for supplying the coolant to the orifices and hence to theinner cutting edge of the wheel;

FIGURE 8 is a diagram representing a method of the present inventionutilizing the diamond surfacing;

FIGURE 9 is a side elevational view of a single diamond grinding stationfor use in the present invention;

FIGURE 10 is also a side elevational view of a single grinding stationfor use in the method and apparatus of the present invention, the viewalso showing means for feeding the glass through the station; and

FIGURE 11 is a partial plan view of an alternate embodiment of a wheelmatrix grinding surface having a plurality of spaced concentric groovesformed therein and intersecting with radial grooves.

With reference to FIG. 1, segment holders 60 are mounted on generallycircular wheel support 61. Segment holders 60 are plates having slightlycurved outer and inner peripheral edge portions 62 and 63 respectivelywith lateral edge faces 64 and 65 tapering slightly in- There have alsobeen reports of wardly from the outer to the inner edge. Bolts 66 and 67are integral with the upper surface of segment holders 60 and havethreaded outer end portions, these mounting bolts extending throughregistering orifices in the wheel support 61 to mount the segmentholders securely to the wheel support with the aid of nuts on theirthreaded end portions.

Grinding segments 68 are secured to the lower surface or side of segmentholders 60 by brazing to provide a diamond grinding plane extendinggenerally perpendicular to the central axis of the support. As shown,segments 68 are secured to the segment holders one per segment holder.Spaced holes or orifices 69 function to discharge liquid coolant to theinner edges of grinding segments 68. The wheel of FIG. 1 is anapproximately 30 inch diameter wheel.

Radial grooves 70 are provided in the cutting surface of segments 68,which grooves are V-shaped in cross section in the embodiment shown inFIG. 4. These grooves together with the fine hard abrasive grits '72 ofpredetermined grit size embedded in the matrix of these grooved cuttingsegments and the supply of liquid coolant to the wheel grinding surfaceduring the surfacing result in a significant improvement in thesurfacing of the plate glass at the late stations of the grinding methodof my copending application Serial No. 119,444, these late stationsusually employing grit sizes of 200-230 grit size and finer.

Grinding segments 68 are secured to segment holders 60 in such manner asto cooperate with one another to form a continuous or substantiallycontinuous narrow circular grinding face or plane located adjacent theperiphery of the wheel support. The width of each segment of thiscircular arrangement is typically about 0.250 inch, and this circulararrangement of segments is located typically about 1 inch from the outerperipheral edge of the wheel support. The abrasive grits are embeddedand dispersed in the matrix of each segment and as wear proceeds duringthe surfacing are exposed on the surface of the matrix. By reason of thecontinuous circular arrangement of the segments, a maximum number ofabrasive grits are provided at the leading edge 73 and trailing edge 74of the segments.

A cup-type wheel 75 is shown in FIG. 5, this wheel having radial grooves76. As shown, cup wheel 75 has 8 radial grooves each inch wide. Wheel 75is a 3-inch diameter Wheel. Diamond grits 77 are embedded in the matrixof this cup wheel.

With reference to FIG. 8, in a specific embodiment, a sheet of plateglass, which is continuously extruded in the melting furnace, is passedthrough the annealing chamber in conventional and known manner. From theannealing chamber the glass sheet is passed successively to each of theinitial diamond grinding stations, these initial grinding stations beingtypically 3 in number. Principal irregularities present in the surfaceof the glass are removed in these initial grinding stations.

Referring now to FIGS. 9 and 10, the sheet of plate glass is fed throughan initial grinding station 16 by driving rollers 17, 18, 19 and 20shown in FIG. 10. Alternatively, the glass sheet may be blocked,clamped, or otherwise secured to a suitable supporting surface and fedwith the supporting surface through the grinding stations. The grindingstation 16 comprises a generally circular diamond grinding wheel 21having a diameter greater than the width of the glass sheet 15. Grindingwheel 21 is mounted coaxially on a rotatable vertical spindle containedwithin bearing housing 22, wheel 21 being driven by motor 24 which ismounted above Wheel 21 on supporting frame 25 made up of suitablesupporting members. Grinding wheel 21 comprises a generally circularsupport and a plurality of grinding segments having radial grooves inthe segment cutting surface as hereinbefore described and mounted on oneside of the support in a generally circular arrangement adjacent theperipheral edge portion of the support as hereafter described.Supporting frame 25 is supported by main frame 26 of the grindingstation, which also supports bearing housing 22 for the vertical spindleof grinding wheel 21. Base 27 of the grinding station provides a heavyrigid support for the entire apparatus. A suitable coolant tank 28 andassociated coolant pump is provided for recirculating coolant to theworking surface between the grinding wheel 21 and the plate glass 15.The cool-ant is preferably supplied or delivered to the inner cuttingedge of the grinding wheels as previously discussed, for instance bymeans of a hollow spindle.

As shown in FIG. 6, the coolant is pumped from coolant supply tank 28 bymeans of pump 29 through conduit 30 into the central passageway 31 ofhollow shaft spindle $2 for grinding wheel 21, passageway 31 extendingalong the axis of spindle 32 and communicating one end of the spindlewith the opposite end thereof. By reason of the centrifugal forceobtaining as a result of rotation of the wheel 21, the coolant flows inan outwardly direction as indicated by the arrows to the inner cuttingedge and into contact with all of the exposed diamond grit surfaces andthe surfaces of grooved grinding segments 38. As shown in FIG. 7, withthe larger grinding wheels, for instance wheels having diameter of 30"and larger, the coolant is pumped from coolant tank 43 by pump 44through conduits 45 and 48 into ante-chambers 46 and 47 respectivelywhich communicate with a plurality of spaced holes or orifices 49 and 50in the grinding Wheel 51.. The spaced orifices, which communicate oneside of the wheel support with the opposite side thereof, are arrangedin a generally circular arrangement adjacent and inwardly of the inneredge of the circular or generally circular arrangement of grooveddiamond segments and function to dischage the coolant to the inner edgeof the grinding segments 52, whereby the centrifugal force resultingfrom rotation of wheel 51 causes the coolant to flow in an outwardlydirection as indicated by the arrows to the inner cutting edge and intocontact with all of the exposed diamond grit surfaces and the surfacesof grinding segments 52.

Grinding segments 68, shown in FIG. 4, each have typical dimensions oflength of about 1 width of about 0.230, and depth or thickness of about/8. The area of the grinding face of each segment 68 is typically about0.415 square inch. Segment holders 60 each have typical dimensions oflength of 1 where segments are attached, width of 2 and thickness of 7In the initial grinding stations, the surface of the Plate glass isroughly ground to remove the principal irregularities in the surface ofthe glass. As disclosed in FIG. 8, the diamond concentration, in termsof carats per cubic inch of wheel matrix, is relatively low in theinitial stations, usually the first three stations. However, the diamondgrit or mesh size should be relatively large in these initial stations.The expressions grit size and mesh size are used synonymously hereinreferring to particles or grits passing through sieves of the specifiednumber of linear openings per inch. Recently sieves of good precision,with openings smaller than 325 mesh have become available, and thisinvention includes in part the use of grits of such smaller size.

Specifically, diamod concentrations of less than 20, preferably about 9carats per cubic inch of grinding segment matrix may be utilized for theinitial stations. The grit size is preferably about the 50 to 60 gritsize inasmuch as the larger grit sizes, say of the order of 20 to 30,tend to cause excessive chipping of the edges of the plate glass.Further, in these initial stations, typical operating conditions are afeed speed of about 200" per minute of the glass relative to thegrinding wheel, and a cut of about .004". The grit size figuresspecified indicates that the diamond grits will pass through a screen ofa certain mesh size but will not pass the screen of the next mesh size.Thus, for example, 50 to 60 grit diamonds will pass through a 50 meshscreen but will not pass through a 60 mesh screen. The basis for meshsizes in the present specification is the US. Sieve Series.

Further, as shown in FIG. 8, as the sheet of plate glass advances fromthe initial grinding stations to additional successive grindingstations, where additional increments of stock are removed from theplate glass, the concentration of diamonds in carats per cubic inch ofwheel matrix is increased, i.e., is higher in these additionalsuccessive stations than in the initial stations. Further, there is acorresponding reduction in size of the diamond particles and a reductionin the depth of the cuts. Diamond concentrations of about carats andhigher, preferably about 20 carats per cubic inch of grinding segmentmatrix are employed in the wheels of the additional successive stations.The average grit size at these intermediate or additional successivestations is about 100120 grit size. Typical operating conditions inthese intermediate or additional successive stations, which are usuallyStations No. 4-7 of the present invention, are a feed speed of about200" per minute of glass relative to the grinding wheel, and a cut ofabout .002".

As shown in FIG. 8, the glass sheet is then advanced to the later orlate grinding stations, these late grinding stations usually beingStations No. 8-14. It is found that employment of low concentrations ofdiamond grits in these later or late stations materially lower thanemployed in the additional successive stages, with the gritssubstantially uniformly dispersed and bonded in the grinding segmentmatrix, gives excellent grinding results with a striking economy indiamond requirements and a considerable reduction in surfacing costs.The use of these lower concentrations of diamond grits with good resultsin the late stations is directly contra to what was previously believed.Diamond concentrations which can be materially lower than 9 carats,preferably lower than 1 carat per cubic inch of grinding segment matrix,are employed in the wheels of these late stations. This reduction indiamond requirements can be readily seen from the following Table III.

TABLE III Typical plate glass grinding with diamonds In each case newpolished plate glass was used for a test. However, it is believed thatlate station grinding of glass previously ground with coarser gritdiamonds would generally afford longer wheel life, require less spindlepower, and give operation with less tendency to glass breakage; thus,all wheel life figures in Table III for the late stations must beconsidered conservative.

As regards the data presented in Table III, the data given for OptimumWidth of Cutting Face of Wheel, Surface Finish, and Wheel Life wereactually measured at Stations 1, 2, 3, 5, 7, 8, 10 and 12. The data forStations 4, 6, 9, 11 were interpolated and those for Stations 13 and 14were extrapolated. The surprisingly low diamond concentrations of theStation 10 and 12 data were particularly interesting.

Diamond grinding in accordance with this invention, as shown in TableIII, requires typically ten stages to replace the conventionaltwenty-eight sand grinding stages. Diamond grinding stages Nos. 11 to 14replace on the order of two-thirds of the conventional iron oxide orrouge polishing stages; about fifteen additional rouge stages inaccordance with conventional methods for final polishing of plate glassare suflicient after the fourteen diamond grinding stages.

The considerable reduction in diamond requirements for the wheels of thelate stations is readily apparent from the data of Table III, the wheelsof late Stations 10-14 having optimum diamond concentrations of fromonly 1 carat per cubic inch of matrix down to as low as .05 carat percubic inch of matrix as contrasted with the wheels of initial Stations1-3 and additional successive Stations 47 having a considerably higherdiamond concentration. Concentrations of diamonds as low as .05 caratper cubic inch and even lower can be used with satisfactory results inthe wheels of the late stations in accordance with this invention. Inconnection with these late stations, it was found to be of the utmostimportance to control within close limits the number of concentration ofdiamond grits in the leading and trailing edges of the wheel.

Optimum WHEEL LIFE Diamond Width of Glass Surface Station Grit SizeConcen- Cutting Removal Finish No. tration in Face of (Mils) (Miero- Ft.1 of In. 3 0t Carats/In. Wheel inches) Glass] Glass] (Mils) Carat CaratIn the tests of Table III a 3-inch outer diameter cup wheel was used(actually 2% inch outer diameter of the grinding surface). Two inch by18 inch glass specimens were moved reversibly in the long direction at afeed speed of 200 inches per minute. Coolant concentration and flow ratewere maintained constant during the periods of the tests.

The conclusions regarding preferred diamond concentrations embodied inthe Table III programming resulted in considerable part from experimentsshowing superior wheel performance at the specified diamondconcentrations than found at higher or lower concentrations. In general,favorable grinding performance under each condition was found for aparticular range of diamond con- TABLE IV from the melting furnace androllers is referred to in the data shown in Tables III and IV. Ingeneral, the number of stages necessary for grinding of any materialdepends on the initial roughness of its surface. For material withsmoother surface than glass from the melting furnace, the initial stagesdescribed in Table III will be unnecessary and may be omitted. Forexample, if it is desired to convert sheet glass to plate glass by aglass re- Efiect of varying diamond concentration on wheel performance[All tests at table speed of 200" per minute.

3 outer diameter cup wheels used] Diamond Wheel Net Average GlassPreferred Conoentra- Life Spindle Surface Breakage Sequence Diamond GritSize tion (Carats! (cu. in. of Power Finish thick of Tests Concencu. in.of glass carat) (Watts) (Mieroglass) tration matrix) inches) (percent)Range 3 1, 067 I97 74. 2 6 2,324 268 55. 8 9 2, 593 320 47. 8 30 1, 250520 42 50 1, 323 600 42 5 to 50. 70 77 630 39 0. 5 2, 388 370 1 2, 678450 21 1.5 3, 900 503 18 3 3, 216 570 18 6 1, 403 725 21 9 1,041 854 2520 .5 to 9. 20 621 768 29 40 68 1, 250 33 100 60 2 Excessive 100 1Downfeed.004 per table reversal. Coolant Cone-:1. 2 Downieed.002 pertable reversal. Coolant Conc.25:1. 3 Downieed-.001 per table reversal.Coolant Conc.-25:1. 4 Downleed.0005 per table reversal. CoolantCone-25:1. 5 Downfeed.0002 per table reversal. Coolant Comm-25:1.

The Table IV data shows a relatively narrow preferred diamondconcentration range for 5060 grit diamonds of 7.5 to 18 and somewhatbroader satisfactory concentration results for additional grinding withsmaller sized grits. Thus, for 100-120 grit size satisfactory grindingtook place at 15 to diamond concentration but not at 9 diamondconcentration, for 200-230 grit size satisfactory grinding took place at5 to 50 diamond concentration but not at 70 diamond concentration, andfor 500 grit size favorable grinding took place at .5 to 9concentration, unsatisfactory grinding at 20 concentration, andextremely bad operation at 40 and 60 concentration. For 1050 grit size,favorable grinding took place at the remarkably low.v

diamond concentration of .05 to 3 carats per cubic inch.

For the 200-230 grit size and 500 grit size diamonds the sequence inwhich the tests were run is given. The order of the experiments showshow completely unexpected were the superior wheel performance resultswith .low diamond concentrations at the late stations. With anyparticular size grit the type of diamonds and wheel construction methodswere kept identical for all diamond concentrations, so that for eachsize the results for different concentrations are completely comparable.

It will be understood that grinding of glass as delivered Diamonds in 30to 50 ,1 size range. Diamonds in 8 to 25 n size range.

moval of 5 to 10 mils (rather than approximately 25 mils as usedaccording to Table III), the first 4 01I5 stations of Table III may beomitted and glass with a surface finish of 2 to 3 micro-inches may beobtained by following the teachings of this table regarding the otherstations.

These ranges in the preferred number of diamonds on the cutting surfaceas has been discussed apply for any annular width of the grindingsurface on the wheel, for example, a width of of 12", providedessentially all of the circumference of the wheel contains a diamondgrinding surface. With conventional wheel making procedures a width ofabout A" is preferred.

Referring again to FIG. 8, from the diamond grinding stages, the plateglass sheet is then advanced to iron oxide or rouge polishing stations,where it is polished in conventional and known manner. The polishingheads at the polishing stations also have vertical spindles and ironoxide or rouge is employed as an abrasive. By virtue of the presentinvention, the number of iron oxide polishing stations required isreduced or lowered considerably as contrasted to the 42 polishingstations previously required.

After completion of the grinding and polishing of one side of the plateglass, the plate glass is reversed or turned over, blocked and passedthrough the second side 13 diamond grinding stations and iron oxidepolishing stations, also shown in FIG. 8, and similar in structure andnumber as those employed for grinding and polishing the first side. Thegrinding and polishing of both sides of the plate glass sheet are thencompleted.

As pointed out in co-pending application Serial No. 50,352, filed August18, 1960, basic variables involved in glass grinding with diamondgrinding wheels include the rate of feed conveyor speed for the plateglass sheet being ground, and the rate of rotation of the diamondgrinding wheel. The conveyor speed or rate of feed of the glass isnormally given in terms of inches per minute. Conveyor speeds of 200inches per minute and higher are practical in the present invention.However, lower speeds of about 175 inches per minute and lower can alsobe employed. The rate of rotation of the diamond grinding wheel in termsof revolutions per minute is not particularly significant, as the rateor speed at which the grinding surface engages the plate glass is alsodependent on the radius of the wheel. With the diamond grinding surfacebeing concentrated near the outer periphery of the grinding wheel, amore useful value is the rate at which the diamond grinding surfacepasses over and engages the plate glass, in terms of surface feet perminute. This is equal to the circumference of the wheel multiplied bythe number of revolutions per unit time of the wheel. Thus, with a wheelhaving a diameter of about feet, the rate of rotation is about 90' to 95revolutions per minute in order to produce a relative veocity betweenthe glass and the diamond grinding surface of about 2800 or 3000 surfacefeet per minute. The stress produced in the glass during the grinding isalso a factor of importance, inasmuch as chipping or breakage of glassresulting from high stresses cannot be tolerated to any significantextent. High stresses are produced in the glass with attendant glasschipping or breakage by use of excessively high diamond concentrationswhen large amounts of stock are to be removed at initial stations in thegrinding process. Use of diamond particle sizes which are too large alsoresults in chipping or breakage of the glass. Further, use of leancoolant concentrations are accompanied by an increase in the grindingstresses. The spindle power which is absorbed in indicative of thestresses, and the likelihood of glass chipping or breakage.

The diamond grinding wheels of this invention can have a circular orgenerally circular wheel support as large as 2 feet, 12 feet, or lagerdiameter.

There appears to be at all the stages in the diamond grinding of plateglass an optimum pressure for each diamond particle, decreasing withdecrease in the average diamond particle size.

The term diamonds or diamond is used herein in a broad sense to includeboth natural diamonds and synthetic diamonds having the approximatehardness or other abrasive qualities of natural diamonds. Diamondconcentrations have been given in carats per cubic inch, with the carat,which is equal to one-fifth of a gram, being the usual unit of diamondweight. With other abrasives which are not of gem quality, it isregarded as suitable to express concentrations as grams per cubic inch.

An example of the use of cubic boron nitride for plate glass grinding atlow concentrations in accordance with this invention is now given. Theglass from the melting furnace is ground with diamond wheels for thefirst 9 stations similarly as previously described in Table III. Wheelsare prepared for Stations 10 to 14, in which cubic boron nitride inequal quantities respectively takes the place of the diamonds and inwhich the same metalbonding and use of a coolant are provided. Operationwith cubic boron nitride wheels is carried out to the same glass removaland surface finish as prescribed in 14 Table III for Stations 10 to 14.Satisfactory grinding and favorable wheel lives are obtained for thesesegmented cubic boron nitride wheels, these wheels containing theabrasives bonded in the wheel matrix in a concentration less than 1 gramper cubic inch of matrix, with the abrasive grits each being less than50 microns in size.

In honing surfaces and/or edges of materials in accordance with thisinvention, the surfaces and/ or edge of the material is ground with agrinding wheel having a low concentration of hard abrasive grits bondedin the grinding surface of the wheel matrix. The abrasive grits arethose characterized by having a hardness of 8 or higher, preferably 12or higher on the Extension of Mohs Scale. Preferred among these hardabrasives are diamonds and cubic boron nitride. The materials which canbe honed include metals, for instance, ferrous metals, e.g., iron andsteels, stone, glass, ceramics, and cemented carbides. The edges ofthese materials which can be honed include the edges immediatelyadjacent and defining holes or orifices. When grinding the surfaceand/or edge of the material to be honed with a grinding wheel havingcubic boron nitride bonded in the grinding surface of the wheel matrix,low concentrations of cubic boron nitride less than 1 gram per cubicinch of matrix can be used. When using a grinding wheel for the honinghaving diamond grits bonded in the wheel matrix, low concentrations ofdiamonds of less than 2 carats per cubic inch of matrix can be used. Bythe term honing used herein is meant converting a non-smooth orirregular surface or edge into a smooth even surface or edge,substantially free of irregularities. Honing includes the sharpening ofedges of materials, for instance the edges of metallic objects, e.g.,ferrous metal cutting blades.

The following examples further illustrate the invention. In all of theexamples the grooves were wide and positioned radially at approximatelyeven spacings on the cutting surfaces of the wheels.

For example, the number and disposition of grooves used may be:

Four wide radial grooves at intervals in the cutting surface of thewheel.

Eight wide grooves as above, at 45 intervals.

Sixteen- A wide grooves as above, at 22 /2" intervals.

Thirty-two wide grooves as above, at 1l A intervals.

Forty-eight wide grooves as above, at 5% intervals.

Ninety-six wide grooves as above, at 2 7 5 intervals.

The grooves extended from the inner to the outer circumference of thecutting surface. New polished glass was used for each test. In each testof Examples I, II and III the table speed was 200 inch/minute and thecoolant flow rate was maintained at 3.0 gals. per minute.

EXAMPLE I The purpose of this example is to show the performance ofcomparable wheels with very fine hard abrasives with and withoutgrooves.

The performance of 3" OD. Wheels containing 1050 grit size diamonds(8-25 micron powder) and having various diamond concentrations are givenin Table V. All grooved wheels are distinguished from those wheelswithout grooves in the tables.

TABLE v 1050 grit size (8-25 m ic1'0ns)-3" O.D. wheels Diamond (3011-Wheel Face Diamond Net Average centration Downfced Width Life, Cu.Spindle Surface Carats (Inches) (Inches) In. of Glass Power Finish (On.In (Carat) (Watts) (Microinches) Avg. 3, 912 Avg. 520 Avg. 9

Avg. 4, 822 Avg. 480 Avg. 7. 2

Avg. 3, 819 Avg. 550 Avg. 9. 5

1 Four Mu radial grooves in wheel cutting surface. 2 Eight Mu radialgrooves in wheel cutting surface.

The data in Table V show that under comparable conditions, for diamondconcentrations of 1.5 and 0.5 carats/cu. in. the insertion of four Widegrooves more than doubled the diamond life of these wheels. At diamondconcentrations of 0.25 carat/cu. in. without grooves, the wheels couldnot be operated at nominal downfeeds without excessive burnishing.However, with grooves as described herein, the diamond life of theWheels was typically over 3000 cu. in. of glass/carat at a downfeed of0.0002".

Comparative performances of wheels with and without grooves for 3" OD.500 diamond grit wheels are given in Table VI. The grooved wheels hadfour A wide radial grooves spaced at 90 intervals.

TABLE VI 500 grit size (-50 microns)3" 0.D. wheels Spindle Speed=3600R.P.M. Glass Specimens-2" X 18' Downfeed:0.0005"/ table reversal *Noradial grooves in wheel surface.

The diamond concentration on all wheels was 1.5 carats/cu. in. which wasevaluated as the optimum diamond concentration.

The data of Table VI confirms the statement of Exam- 'ple I that adiamond life of over 3000 cu. in. of glass/ carat is possible with allgrit sizes from 50/ 60 to 1050.

EXAMPLE II grooves were cut to give 16 grooves, followed by sufficienttesting to obtain the result indicated. Additional grooves were then cuton the same wheel to obtain the 32-groove results.

TABLE VII Efiect of number of grooves Spindle Speed=4400 r.p.m.DoWnIeed=.0001/table reversal Glass Specimens=2 x 18 Diamond Not SpindleAverage No. of Grooves Life (cu. in. Power Surface of glass (Watts)Finish carat) (Microinchcs) 8 Unsatisfactory operation under aboveconditions *Optimum No. of Grooves.

From the data in Table VII it can be seen that the wheel with 16 grooveswas superior to that with 8 grooves and 32 moves.

EXAMPLE III The purpose of this. example is to show the relationshipbetween the number of grooves used for satisfactory performance and thegrit size for wheels of a given size.

Diamond life and surface finish for 3" OD. grooved diamond wheelsDiamond Optimum Downfeed Approx. Diamond Life Net Surface Grit Ooncen- N0. (inches/ Wheel Spindle Finish Size tration Pie Radial table FacePower (Micro- (carats/ Grooves reversal) \Vitlth On. In. of Sq. Ft. of(Watts) inches) cu. in.) (Inches) glass/carat glass/carat In Table VIIIthe performance of the grooved wheels with various grit sizes is given.The optimum number of grooves is given for each grit size. The data inthis table show that as the grit becomes finer, a larger number ofgrooves is necessary.

All wheels shown in Table VIII contain the same bond. The 1500 gritwheel disclosed therein shows a considerably higher diamond life incarats per cubic inch of glass than the 1500 grit wheel disclosed inTable VH. This difference in performance is believed due to a differencein the Wheel bond used.

It should be noted that a diamond life of 1650 cu. in. of glass/caratfor a grit size of 1500 (6-12 microns), despite being less than theglass removal for coarser grit, is favorable. The demonstrated finishingof 115,000 sq. ft. of glass/carat with 1500 grit wheels indicates thatsuch wheels are economic.

EXAMPLE IV The 18" glass specimens used with the 3" wheels is a closerapproximation of the continuous glass application bu-t is still aconservative estimate.

When used in a 30" wheel, a specimen of glass would be equivalent to a6" specimen of glass used with a 3" wheel. A diamond life of only 1600cu. in. of glass per carat was obtained using a specimen of glass 6"long with a 3" OD. wheel. However, if a specimen of glass 18" long isused with a comparable 3" wheel, a diamond wheel life of over 3000 cu.in. of glass per carat can be obtained.

Based on evaluation of wheel life with glass specimens of variouslengths, it has been found that a 1219 cu. in. of glass/carat diamondlife with a 60" specimen in a 30" wheel would be equivalent to a diamondlife of over 3000 cu. in. of glass per carat if the wheel were operatedwith continuous glass lengths.

The data in Table IX show that the number of grooves needed forfavorable performance of the 30" wheels increases as the grit becomesfiner. Comparing the data in Table IX with that in Table VIII, it can beseen that using 500 grit wheels at a diamond concentration of 1.5 caratsper cu. in., the 3" wheel having 4 grooves produced a diamond life ofover 3000 cu. in. of glass per carat and a surface finish of 19microinches, and the 30" wheel having 96 grooves produced comparableresults.

TABLE IX Performance of diamond wheels-approx. 30" OD.

Grit Diamond No.0f M6 Approx. Diamond Net Surface Size Concen- GroovesDownieed Wheel Life Spindle Finish tratlo Face Power carats inches dth(cu. in. of glass (KW) (Microcu. in. table reversal carat inches) Thewheels were assembled from 48 segments, and the segments were assembledto butt closely together making a continuous peripheral wheel. 3/grooves were inserted where the segments articulated. For 96 grooves,one additional V1 groove was inserted in each segment.

2 Average of 4 tests.

to a diamond life of over 3000 cu. in. of glass per carat in the testson 3" OD. wheels using 2 x 18" glass specimens.

The controlling factor was the length of the glass specimen relative tothe size of the wheels. It has been found that glass specimen length hasa considerable effect upon the diamond wheel performance. In testing theperformance of the wheels, with each table reversal the wheel goes offthe glass completely. During the going off and coming on stages abnormalpressures are exerted on the cutting wheel surface. Such pressures havebeen found detrimental to the wheel performance. This problem wouldobviously not be present where continuous glass lengths are used, but ischaracteristic of the laboratory equipment used in these tests.

The 60 glass specimen length used routinely in tests with 30 wheels doesnot simulate the continuous glass length of the ultimate plate glasssurfacing very well. 75

In a wheel matrix grinding surface of FIG. 11, suitably formed, radiallyspaced-apart concentric grooves 81 and 82 intersect a plurality ofradial grooves 83.

- It will be obvious to those skilled in the art that many modificationscan be made in the scope of the present invention without departing fromthe spirit thereof and this invention includes all such modifications.

What is claimed is:

1. A grinding apparatus comprising a rotatable spindle, a diamondgrinding wheel mounted coaxially on the spindle, means for rotating thespindle and hence the diamond grinding wheel, means for feeding plateglass horizontally through the apparatus for surface grinding by thewheel, the wheel comprising a support, a metal matrix on the supportproviding a substantially continuous grinding surface, the matrix havingdiamond grits bonded therein, the diamond grits having a grit sizewithin the range of 1050-1500 grit size, means securing the matrix tothe support, a plurality of spaced radial grooves formed in the wheelmatrix grinding surface, and means for supplying a liquid coolant to thegrinding surface.

2. A grinding apparatus comprising a rotatable spindle, a grinding wheelmounted coaxially on the spindle, means for rotating the spindle andhence the grinding wheel, means for feeding plate glass horizontallythrough the apparatus for surface grinding by the wheel, the wheelcornprising a support, a metal matrix on the support providing asubstantially continuous grinding surface, the matrix having hardabrasive grits bonded therein, the abrasive grits having a grit sizewithin the range of 500-2500 grit size, means securing the matrix to thesupport member, a plurality of spaced radial grooves formed in thematrix grinding surface, and means for supplying a liquid coolant to thegrinding surface.

3. A grinding apparatus comprising a rotatable spindle, a grinding wheelmounted coaxially on the spindle, means for rotating the spindle andhence the grinding wheel, means for feeding glass through the apparatusfor surface grinding by the wheel, the wheel comprising a support, ametal matrix on the support providing a substantially continuousgrinding surface, the matrix having hard abrasive grits bonded therein,the abrasive grits having a grit size not greater than 200-230 gritsize, means securing the matrix to the support, a plurality of spacedradial grooves formed in the wheel matrix grinding surface, and meansfor supplying a liquid coolant to the grinding surface.

4. The grinding apparatus of claim 3 wherein the fine hard abrasivegrits are diamond grits.

5. A grinding apparatus comprising a rotatable spindle, a grinding wheelmounted on the spindle, means for rotating the spindle and hence thegrinding wheel, means for feeding plate glass through the apparatus forsurface grinding by the wheel, the wheel comprising a support, a matrixon the support providing a substantially continuous grinding surface,the matrix having hard abrasive grits of a grit size not greater than200-230 grit size bonded therein, means securing the matrix to thesupport, a plurality of spaced grooves formed in the wheel matrixgrinding surface, and means for supplying a coolant to the wheelgrinding surface.

6. A grinding apparatus comprising a rotatable spindle, a grinding Wheelmounted coaxially on the spindle, means for rotating the spindle andhence the grinding wheel, means for feeding plate glass through theapparatus for surface grinding by the diamond wheel, the Wheelcomprising a support, a matrix on the support providing a substantiallycontinuous grinding surface, the matrix having diamond grits of a gritsize not greater than 200-230 grit size bonded therein, means securingthe matrix to the support, a plurality of spaced radial grooves ofpredetermined width and configuration formed in the wheel matrixgrinding surface for promoting a predetermined distribution of liquidcoolant in intromissive flow across said grinding surface in grindingrelation with the plate glass and means for supplying liquid coolant tothe grinding surface.

7. The apparatus of claim 6 wherein said diamond grits have a grit sizewithin the range of 1050-1500 grit size.

8. The apparatus of claim 6 further characterized by at least oneconcentric group being provided in said Wheel matrix grinding surface,said concentric grooves intersecting said radial grooves.

9. A grinding apparatus including a rotatable spindle, a diamondgrinding wheel mounted coaxially on the spindle, means for rotating thespindle and hence the grinding wheel, means for feeding a fiat sheet ofglass or the like through the apparatus for surface grinding by thediamond wheel, the Wheel comprising a support, a matrix on said supportproviding a substantially continuous grinding surface, said matrixhaving diamond grits of a grit size not greater than 200-230 grit sizebonded therein in a concentration not greater than 9 carats per cubicinch, means for securing said matrix to said support, a plurality ofspaced radial grooves of predetermined width and configuration formed insaid wheel matrix grinding surface for promoting a predetermineddistribution of liquid coolant in intromissive flow across said grindingsurface in grinding relation with the sheet of glass, and means forsupplying liquid coolant to said grinding surface.

10. A grinding apparatus including a rotatable spindle, a diamond wheelmounted coaxially on the spindle, means for rotating the spindle andhence the grinding wheel, means for feeding a flat sheet of glass or thelike through the apparatus for surface grinding by the diamond wheel,the wheel comprising a support, a plurality of adjacent arcuate grindingsegments having exposed matrices forming a substantially continuouscircular grinding surface located adjacent the periphery of saidgrinding wheel support, each of said arcuate grinding segments having atleast one radial groove formed therein intermediate the ends thereof andof a predetermined size and configuration for promoting a predetermineddistribution of liquid coolant in intromissive flow across said grindingsurface in grinding relation with the flat sheet of glass, said matriceshaving diamond grits of a grit size not greater than 200- 230 grit sizebonded therein in a concentration not greater than 9 carats per cubicinch, means for securing said grinding segments to said support, andmeans for supplying the liquid coolant to said grinding surface.

References Cited by the Examiner UNITED STATES PATENTS 1,932,305 10/1933Escole 51-110 2,787,100 4/1957 Peyches 51283 2,823,496 2/1958 Winter51267 X 2,867,063 1/1959 Metzger 51209 2,883,801 4/1959 Dryon 51ll02,942,387 6/ 1960 Lindblad 5 l-209 2,985,898 5/1961 Knost 51-1l0 X2,022,521 7/1961 Glasgow 5l283 3,026,655 3/ 1962 Osenberg 51209 ROBERTC. RIORDON, Primary Examiner.

FRANK H. BRONAUGH, LESTER M. SWINGLE,

J. SPENCER QVERHOLSER, Examiners.

